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Abstract

We present bioinspired artificial compound eye surface structures that consist of antireflective subwavelength structures (SWSs) on hexagonally patterned microstructures (MSs), for the purpose of efficient light escaping inside light-emitting materials/devices. Theoretical understanding and geometrical optimization of SWSs on MSs are described together with rigorous coupled-wave analysis. As a proof of this concept, AlGaInP red light-emitting diodes (LEDs) with SWS/MSs were fabricated, and a light output power enhancement of 72.47% was achieved as compared to that of conventional LEDs. The artificial compound eye structures are not limited to LEDs, and the fabrication process is compatible with most semiconductor device manufacturing processes; hence, this concept opens up new possibilities for improving the optical performance of various optoelectronic device applications.

Figures (6)

Fig. 1 (a) Schematic diagram of four surface structures: (i) a flat surface, (ii) an MS, (iii) an SWS, and (iv) an SWS on an MS. The dashed and solid red arrows indicate the Fresnel internal reflection and total internal reflection, respectively. (b) Calculated internal reflectance of the GaP substrate with and without an SWS as a function of incident angle at a wavelength of 635 nm. (c) Electric field intensity distribution of the SWS on a GaP substrate at 635 nm for incident angles of 0° and 20°.

Fig. 2 (a) Schematic illustration of the fabrication procedure for the SWS/MS architecture. (b) Tilted-angle view of SEM images for the fabricated samples with (i) an MS, (ii) an SWS, and (iii) an SWS/MS on a GaP substrate. (iv) A lower magnification image of (iii).

Fig. 3 (a) Contour plot of the reflectance variation of SWSs on a GaP substrate as a function of SWS wavelength and period. The height of the SWS was set to 300 nm. (b) Electric field intensity distribution of SWSs on a GaP substrate with a period of 200 nm (A) and 300 nm (B) at 635 nm for normal incidence. (c) Contour plot of the reflectance variation of a GaP SWS as a function of the SWS wavelength and height. The period of the SWS was set to 200 nm. (d) Reflectance of a GaP SWS with a period of 200 nm as a function of the SWS height at a wavelength of 635 nm (red line) and 1000 nm (black line). Each arrow indicates the first reflectance dip position, i.e., hdip = 150 nm at a wavelength of 635 nm and hdip = 260 nm at a wavelength of 1000 nm.

Fig. 4 (a) Measured total transmittance of backside illuminated light as a function of wavelength for a GaP substrate with four different surface structures (a flat surface, a MS, a SWS, and an SWS on an MS). To induce randomly diffused light, samples with a slightly roughened back-surface were used. (b) Transmittance enhancement ratio of each sample as measured against a reference sample with a flat surface. (c) Measured total reflectance of GaP substrates with four different surface structures at normal incidence in diffuse mode with an integrating sphere.